System and method for downdraft gasification

ABSTRACT

A downdraft gasifier for producing a gaseous fuel to be used in an engine from a carbonaceous material with a pyrolysis module, a reactor module, and a heat exchanger system that cooperate to produce the gaseous fuel from the carbonaceous material and to extract particulates from the gaseous fuel from the reactor. The heat exchange system includes a first heat exchanger coupled to the dryer module that heats the carbonaceous material with the gaseous fuel output of the reactor module to dry the carbonaceous material; a second heat exchanger coupled to the pyrolysis module that heats the dried carbonaceous material with the exhaust from the engine to pyrolyze the dried carbonaceous material into tar gas and charcoal; and a third heat exchanger coupled to the reactor module that heats air used to combust the tar gas with the gaseous fuel output of the reactor module to preheat the air.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/846,807, filed 29 Jul. 2010, which claims the benefit of U.S.Provisional Application No. 61/229,413 filed 29 Jul. 2009, which areincorporated in their entirety by this reference.

TECHNICAL FIELD

This invention relates generally to the gasifier field, and morespecifically to an improved system and method for downdraft gasificationin the downdraft gasifier field.

BACKGROUND

Gasifiers produce gaseous fuel that may be used in engines (for example,internal combustion engines that may be used to produce electricityand/or power vehicles) from carbonaceous material (for example, biomassand organic waste). Gasifiers conventionally use a combination of thefollowing four reactions: combustion, reduction, pyrolysis, and drying.Fixed bed gasifiers (or “moving bed” gasifiers) are typically arrangedas either an updraft gasifier type or a downdraft gasifier type. Theupdraft gasifier type utilizes the heat from the gas rising up from thecombustion process to reduce, pyrolyze, and dry the carbonaceousmaterial. As shown in FIG. 1, this allows for beneficial heat transferbetween the processes (from high temperature reactions to lowertemperature reactions). However, because the output gas goes through thepyrolyzing and drying processes last, the gas is relatively unclean andmay include volatile tar gases and particulates that must be filteredand prepared before use. The downdraft gasifier type, however, dries thecarbonaceous material, pyrolyzes the dried carbonaceous material intotar gas and charcoal, combusts the volatile tar gas, and finally reducesthe combusted tar gas with the charcoal, thus producing relativelycleaner gaseous fuel than the updraft gasifier type. This may facilitateuse of the gaseous fuel in the engine. However, the thermal and chemicalrelationships between successive stages in the downdraft gasifier areless than ideal for efficiency. For example, as shown in FIG. 2, heat isnecessary to dry the carbonacecous material, but there is no obvioussource of heat from within the downdraft gasification process.Similarly, pyrolysis occurs after drying, but the ideal temperature forpyrolysis is higher than that of drying, also necessitating heat input.Similarly, combustion occurs after pyrolysis, but the ideal temperaturefor combustion is higher than pyrolysis, again necessitating heat input.Also, in downdraft gasifiers where the processes are not adequatelyseparated, higher temperature processes become parasitic loads on lowertemperature processes, decreasing the effectiveness of the gasifier inconverting carbonaceous material into gaseous fuel. For example, thedrying process may become a parasitic load on the pyrolysis process,decreasing the effectiveness of the carbonaceous material to targas/charcoal conversion in the pyrolysis process and/or the pyrolysisprocess becomes a parasitic load on the combustion and/or reductionprocesses, decreasing the conversion effectiveness in the combustionand/or reduction processes. Additionally, gaseous fuel output from thereduction process is typically too hot to be used in an engine, and mustbe cooled. Also, any water content of the carbonaceous material ispreferably substantially fully removed in the drying process to removethe thermal load of heating water in the pyrolysis and combustionprocesses. However, additional water may be beneficial in the reductionprocess, which occurs after the pyrolysis and combustion processes.While a downdraft gasifier may benefit from heat sources and materialtransporters in order to maintain the gasification process, the use ofan external heat source and/or not effectively managing materials withinthe system will significantly decrease the effective carbonaceousmaterial to gaseous fuel conversion of a downdraft gasifier and maydecrease the viability of using the downdraft gasifier as an alternativeenergy source. Prior attempts in heat management within downdraftgasifiers (for example, using waste heat from one process to heatanother) have also been substantially complicated, included manycomponents, and expensive. Thus, there is a need in the downdraftgasifier field to create an improved system and method for heat andmaterial management within a downdraft gasifier.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is schematic representation of the ideal thermal and processrelationships within an updraft gasifier.

FIG. 2 is a schematic representation of the ideal material and processrelationships within a downdraft gasifier.

FIG. 3 is a schematic representation of the downdraft gasifier of thepreferred embodiments.

FIG. 4 is an exploded isometric view of the downdraft gasifier of thepreferred embodiments.

FIG. 5 is a schematic representation of method for heat management indowndraft gasifier of the preferred embodiments and the heat transferrelationships within the downdraft gasifier of the preferredembodiments.

FIGS. 6a and 6b are schematic representations of alternativearrangements of the downdraft gasifier of the preferred embodiments.

FIG. 7 is an exploded view of the dryer module of the preferredembodiments.

FIG. 8 is an exploded view of the pyrolysis module of the preferredembodiments.

FIG. 9 is an exploded view of the reactor module and gas cowling of thepreferred embodiments.

FIG. 10 is an exploded view of the heat extractor.

FIG. 11 is a schematic representation of an alternative arrangement ofthe downdraft gasifier of the preferred embodiments with the pyrolysismodule and dryer module combined.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiments of the inventionis not intended to limit the invention to these preferred embodiments,but rather to enable any person skilled in the art to make and use thisinvention.

As shown in FIGS. 3 and 4, the downdraft gasifier 100 of the preferredembodiments produces a gaseous fuel to be used in an engine fromcarbonaceous material, and includes a dryer module 110, a pyrolysismodule 120, a reactor module 130, and a heat exchanger system 200 thatcooperate to produce the gaseous fuel from the carbonaceous material andto extract particulates from the gaseous fuel. The heat exchanger systempreferably includes a first heat exchanger 210 coupled to the dryermodule 110 that heats the carbonaceous material with the gaseous fueloutput of the reactor module 130 to dry the carbonaceous material andextract heat from the gaseous fuel; a second heat exchanger 220 coupledto the pyrolysis module 120 that heats the dried carbonaceous materialwith exhaust from the engine to pryolyze the dried carbonaceous materialinto tar gas and charcoal; and a third heat exchanger 330 coupled to thereactor module 130 that heats air used to combust the tar gas withgaseous fuel output of the reactor module 130 to preheat the air and toextract heat from the gaseous fuel output of the reactor module 130. Asshown in FIG. 3, the downdraft gasifier 100 may also include a heatextractor 140 that further extracts heat from the gaseous fuel from thereactor module. The heat extractor 140 preferably includes a gaseousfuel inlet 144 that receives gaseous fuel from the reactor module, agaseous fuel path 146 within the heat extractor 140 that extracts heatfrom the gaseous fuel, and a gaseous fuel outlet 148 that delivers gasto the first heat exchanger 210. The heat extractor 140 may include acyclone module 142 that cooperates with the dryer module 110, thepyrolysis module 120, and the reactor module 130 to further extractparticulates from the gaseous fuel. The heat extractor 140 may alsoinclude a fourth heat exchanger 240 that exchanges heat with the gaseousfuel to extract heat from the gaseous fuel. The fourth heat exchanger240 may be coupled to the cyclone module 142. The fourth heat exchanger240 may heat water with the gaseous fuel from the reactor module to heatand/or vaporize the water and to further extract heat from the gaseousfuel. The vaporized water may then be injected into the reactor module130 to be used in reduction of the combusted tar gas with charcoal. Thedowndraft gasifier 100 may also include a filter 150 that furtherremoves particulates and contaminants from the gaseous fuel output ofthe gasifier 100.

As shown in FIG. 5, the method S100, for managing heat within adowndraft gasifier for producing a gaseous fuel from the carbonaceousmaterial to be used in an engine preferably includes drying thecarbonaceous material with the heat from the gaseous fuel output in adryer module to produce dried carbonaceous material Step S110,pyrolyzing the dried carbonaceous material with the heat from theexhaust of the engine in a pyrolysis module to produce tar gas andcharcoal Step S120, combusting the tar gas with air and reducing thecombusted tar gas with the charcoal in a reactor module to producegaseous fuel Step S130, preheating the air used to combust the tar gaswith the gaseous fuel post reduction Step S140, and extracting heat postreduction prior to using the heat from the gaseous fuel to dry thecarbonaceous material Step S150. The step of extracting heat postreduction prior to using the heat from the gaseous fuel to dry thecarbonaceous material S150 may include the step of extractingparticulates from the gaseous fuel in a cyclone module. The step ofextracting heat post reduction S150 may also include the steps ofvaporizing water with the heat from the gaseous fuel post reduction StepS160 and injecting the vaporized water into the reactor to be used inreduction Step S162. Extracting heat post reduction prior to using theheat from the gaseous fuel to dry the carbonaceous material Step S150may alternatively be combined with preheating the air used to combustthe tar gas with the gaseous fuel post reduction Step S140, for example,in variations of the downdraft gasifier 100 where preheating the airused to combust the tar gas decreases the temperature of the gaseousfuel post reduction to a suitable temperature for drying thecarbonaceous material.

The dryer module 110 functions as the location where the incomingcarbonaceous material is dried. More specifically, water content isremoved from the carbonaceous material in the dryer module no. Thecarbonaceous material may be any suitable type of material that includescarbon, for example, biomass (such as wood, plants, or algae),biodegradable waste (such as any waste generated by a plant or anima),and coal. The dryer module 110 preferably includes a carbonaceous fuelinlet 114 that allows carbonaceous fuel to enter the dryer module 110and a carbonaceous fuel outlet 116 that allows the dried carbonaceousfuel to exit. The dried carbonaceous fuel is then preferably transportedto the pyrolysis module 120 for pyrolyzing. As shown in FIG. 3, thedryer module no preferably includes a drying portion in that containsthe carbonaceous material and a condensing portion 112 (also referred toas the “monorator hopper”). The condensing portion 112 is preferablyarranged substantially above and in fluid communication with the dryingportion 111. As the carbonaceous material is heated by the gaseousoutput of the reactor module 130, water content of the carbonaceousmaterial is vaporized and rises upwards out of the drying portion in andinto the monorator hopper 112. As the vaporized water contacts the wallof the monorator hopper 112, the water condenses and is removed from thecarbonaceous material. By allowing the water to condense in a locationaway from the carbonaceous material, the amount of water that condensesback onto the carbonaceous material is substantially decreased. If wateris allowed to condense back onto the carbonaceous material that is thentransported into the pyrolysis module to be pyrolyzed, the extraneouswater functions to increase the thermal load on the pyrolysis module,decreasing the efficiency of the pyrolysis process and the overallefficiency of the gasifier. Thus, the use of a condensing portion 112that is removed from the carbonaceous material is substantiallybeneficial and advantageous. However, any other suitable arrangement ofthe dryer module 110 may be used.

The dryer module no is preferably of a generally cylindrical structure,but may alternatively be any other suitable geometry. The condensationportion 112 of the dryer module 110 is preferably of a larger diameterthan the drying portion 111 to substantially prevent condensed water onthe wall of the condensation portion 112 to fall back into the dryingportion 111. However, the drying portion in and the condensation portion112 may be of any other suitable arrangement. The cylindrical structureof the drying portion 111 preferably includes an inner jacket 118 thatis formed by rolling a continuous piece of sheet metal and preferablyincludes flange rings coupled to the ends of the cylinder formed by thesheet metal and end plates fastened (for example, using nuts and boltsor any other suitable type of fastener) to the sheet metal and flangerings that substantially maintain the rolled shape of the sheet metal.The drying portion 111 preferably also includes an outer jacket 119 thatis constructed using similar or identical materials and methods as theinner jacket that cooperates with the inner jacket to define an annularspace between the inner and outer jackets. Similarly, the condensingportion 112 is also preferably constructed using similar or identicalmaterials and methods as the inner jacket, and is preferably coupled tothe drying portion 111 through the endplates. However, any othersuitable construction of the dryer module 110 may be used. The sheetmetal, endplates, and flange rings are preferably of a steel material,but may alternatively be aluminum, titanium, or any other suitable typeof metal. Alternatively, the drying portion 111 may also be of squaretype or trapezoidal type structure, similarly constructed of sheet metaland end plates. However, any other suitable shape for the drying portion111, condensing portion 112, or the dryer module no may be used.

The dryer module no is preferably separate from and arrangedsubstantially adjacent to the pyrolysis module 120, as shown in FIG. 3,decreasing the water content that is transported with the driedcarbonaceous material into the pyrolysis module 120. The downdraftgasifier 100 may include an auger that transports the dried carbonaceousmaterial into the pyrolysis module 120. The rotation speed of the augermay be varied depending on the desired output of the gasifier (which mayfacilitate cleaner start ups and shut downs), the existing carbonaceousmaterial content within the gasifier, and/or any other suitable factor.The auger may be hand driven, but may alternatively be coupled to amotor that automatically rotates the auger to regulate the carbonaceousmaterial within the gasifier. However, any other suitable type oftransporter may be used for the carbonaceous material. Alternatively,the dryer module 110 may be arranged above the pyrolysis module 120, asshown in FIG. 6. In this variation, gravity may be used to drop driedcarbonaceous material into the pyrolysis module 120, decreasing the needfor a driven material transporter and potentially decreasing the energyrequired to run the gasifier. Additionally, certain carbonaceousmaterial may be difficult to transport using an auger. By utilizinggravity, material transport may be simplified and facilitated. Becausewater vapor condenses upwards, the water content of the carbonaceousmaterial in this variation is substantially removed from thecarbonaceous material prior to pyrolysis. However, any other suitablearrangement of the dryer module 110 relative to the pyrolysis module 120may be used.

The first heat exchanger 210 is preferably arranged substantially withinthe annular space defined by the inner and outer jacket of the dryermodule no. The first heat exchanger 210 preferably includes a gaseousfuel inlet 212, a gaseous fuel path 214, and a gaseous fuel outlet 216.The gaseous fuel inlet 212 is may coupled directly to the third heatexchanger 230, but may alternatively be coupled to the heat extractor140 to receive gaseous fuel that has been cooled by the heat extractor140. The temperature of the gaseous fuel that exits directly from thereduction reaction in typical gasifers may be around 600° C. As furtherdescribed below, the third heat exchanger may decrease the temperatureof the gaseous fuel output of the reactor to around 200° C.-300° C.However, carbonaceous material may pyrolyze under this temperaturerange. As a result, it may be beneficial to further extract heat fromthe gaseous fuel output through the heat extractor 140 prior to heatingthe carbonaceous material with the gaseous fuel output, substantiallyisolating pyrolysis from drying. The temperature range of the gaseousfuel that is received by the gaseous fuel inlet 212 is preferably around100° C.-220° C. More specifically, a temperature range of around 150°C.-220° C. may increase the drying rate without inducing pyrolysis.However, any other suitable temperature may be used.

The gaseous fuel path 214 of the first heat exchanger 210 preferablytraverses about the dryer module 110 at least once, for example, in azigzag pattern back and forth about the dryer module no. The zigzagpattern may traverse across a portion of the surface area of outer wallof the inner jacket of the dryer module no, but may alternativelytraverse across substantially the whole surface area the outer wall ofthe inner jacket of the dryer module no. The zigzag pattern may increasethe efficiency of heat transfer from the gaseous fuel into the dryingportion 111 to the carbonaceous material. The zigzag pattern also allowsfor cross-current flow, which also may increase heat transferefficiency. Additionally, the zigzag pattern may also facilitate inbreaking laminar flow within the gaseous fuel to increase heat transferand particulate extraction from the gaseous fuel. However, any othersuitable gaseous flow path may be used. The outer wall of the innerjacket and the inner wall of the outer jacket and the drying portion 111preferably cooperatively define the gaseous flow path 214. To define thetraversing pattern of the gaseous flow path 214, the inner wall of theouter jacket preferably includes baffles that cooperate with the outerwall of the inner jacket to define the gaseous fuel path and to directthe gaseous fuel in a traversing manner. However, the gaseous fuel path214 may be defined using any other suitable material or method.

The gaseous fuel outlet 216 of the first heat exchanger 210 functions asthe outlet of the gaseous fuel output of the downdraft gasifier 100.More specifically, the final product of the downdraft gasifier 100 isoutputted through the gaseous fuel outlet 216 of the first heatexchanger 210. Through the first heat exchanger 210, the gaseous fuel ispreferably cooled down to a temperature that is suitable to be used, forexample, in an engine. As described above, gaseous fuel that is receivedin the gaseous fuel inlet 212 may be of a temperature within the rangeof 100° C.-220° C., which is too hot to be used in typical applications.Through using the heat from the gaseous fuel to dry the carbonaceousfuel, the gaseous fuel may be further cooled down to about 40° C., whichis suitable for use in an engine. The downdraft gasifier 100 of thepreferred embodiments utilizes heat from the gaseous fuel output to drycarbonaceous fuel, thereby cooling gaseous fuel output to a usabletemperature and reducing the need for an external cooling system.However, any other suitable heat transfer and temperature relationshipwithin the first heat exchanger 210 may be used. To further clean thegaseous fuel prior to use, the gaseous fuel outlet 216 may be coupled toa filter 150, as shown in FIGS. 3 and 4. The filter 150 may alsofunction further cool the gaseous fuel.

The pyrolysis module 120 is preferably where the dried carbonaceousmaterial is pyrolyzed into tar gas and charcoal. More specifically, thecarbonaceous material is heated at a substantially high temperature(typically above 200° C.), in the substantial absence of oxygen, thusburning the carbonaceous material into volatile tar gas and charcoal.The volatility of tar gas and charcoal contributes substantially tolater processes in gasification. The pyrolysis module 120 preferablyincludes a dried carbonaceous fuel inlet 122 that allows driedcarbonaceous fuel from the dryer module 110 to enter the pyrolysismodule 120 and a tar gas and charcoal outlet 128 that allows the tar gasand charcoal to exit the pyrolysis module 120, preferably into thereactor module 130. Similar to the drying portion of the dryer modulein, the pyrolysis module 120 preferably also of a generally cylindricalstructure that includes an inner jacket 126 and an outer jacket 125 thatcooperatively define an annual space in between the inner jacket and theouter jacket. The pyrolysis module 120 is preferably constructed usingsimilar or identical materials and methods as described above for thedryer module 110, but may alternatively be constructed using any othersuitable material and method.

The pyrolysis module 120 is preferably arranged above the reactor module130 and is preferably attached to the reactor module 130 through flangerings and endplates, substantially similar to how the condensing portion112 is attached to the drying portion in of the dryer module no.However, any other suitable method of arranging the pyrolysis module 120above the reactor module 130 may be used. As shown in FIG. 3, the targas and charcoal outlet 128 of the pyrolysis module 120 preferablyextends into the reactor module 130, allowing tar gas and charcoal toexit the pyrolysis module 120 and directly into the reactor module 130through gravity. The tar gas and charcoal outlet 128 may also include amotor 124 that drives the movement of the tar gas and charcoal into thereactor module 130. By controlling the amount of tar gas/charcoal mayfacilitate cleaner start ups and shut downs of the gasifier (forexample, less unused carbonaceous material inside the reactor).Alternatively, the push force from additional tar gas and charcoalgenerated during pyrolysis and gravity may be used to naturally push thepreviously generated tar gas and charcoal out through the tar gas andcharcoal outlet 128 into the reactor module 130. However, the tar gasand charcoal may be transported from the pyrolysis module 120 to thereactor module 130 using any other suitable method. While the tar gasand charcoal outlet 128 of the pyrolysis module 120 may extend into thereactor module, the heat from the reactor module 130 preferably does notsubstantially affect heat within the pyrolysis module 120, thusdecreasing the thermal load on the reactor module 130. The depth thatthe tar gas and charcoal outlet 128 extends into the reactor ispreferably where the temperature of the pyrolysis module 120 issubstantially higher than that of the reactor module 130 at thatparticular level, discouraging heat transfer from the reactor module 130into the pyrolysis module 120. However, any other suitable arrangementof the pyrolysis module 120 may be used.

The second heat exchanger 220 is preferably arranged substantiallywithin the annular space defined by the inner and outer jackets of thepyrolysis module 120. The second heat exchanger 220 preferably includesan exhaust gas inlet 222, an exhaust gas path 224, and an exhaust gasoutlet 226. The exhaust gas inlet 222 is preferably coupled to anengine, preferably, the engine that uses the gaseous fuel output fromthe gasifier, but may alternatively be any other suitable engine, andreceives exhaust gas from the engine. The temperature of the exhaust gasthat enters the exhaust gas inlet 222 may in the range of 600° C.-700°C. and the exhaust gas preferably contains enough heat energy to heatthe dried carbonaceous material to temperatures that pyrolyze the driedcarbonaceous material into tar gas and charcoal. Temperatures necessaryto pyrolyze carbonaceous material may vary depending on the type ofcarbonaceous material, but are generally above 200° C. The exhaust gaspath 224 is preferably substantially similar or identical to the gaseousfuel path 214 of the first heat exchanger 210 and traverses about thepyrolysis module 220 in a zigzag pattern. The exhaust gas path 224 isalso preferably cooperatively defined by the inner and outer jackets ofthe pyrolysis module 220. As shown in FIG. 7, the exhaust gas path 224may be preferably allows the exhaust gas inlet 222 and the exhaust gasoutlet 226 to be on substantially the same level, allowing heat to beconcentrated in substantial one region within the pyrolysis module anddecreasing the size of the pyrolysis module 120. To spread air along thesurface of the inner jacket 122, the inner and outer jackets maycooperative define baffles that divert incoming air towards a particulardirection as opposed to defining an actual path, as shown in FIG. 7.However, the exhaust gas path 224 may traverse about the pyrolysismodule 220 in any other suitable pattern and may be defined using anyother suitable material and method. The exhaust gas outlet 226preferably outputs the cooled exhaust gas to the ambient environment. Inthe second heat exchanger 220, the heat energy within the exhaust gasthat would otherwise become wasted energy is used as a heat input toinduce pyrolysis.

In certain usage scenarios, too much tar gas may be produced relative tothe charcoal in the pyrolysis module 120. Too much tar gas relative tothe charcoal may result in an imbalance between the combustion andreduction processes. To address this possible usage scenario, thepyrolysis module 120 may include a tar gas outlet that allows extra targas to exit the pyrolysis module to a burning module. The burning modulepreferably “burns” or combusts the tar gas, decreasing the volatility ofthe tar gas. As a result of the burning, the burned tar gas is at asubstantially high temperature. The second heat exchanger may alsoinclude a burned tar gas inlet that routes the burned tar gas back tothe pyrolysis module 120 to heat and pyrolyze the dried carbonaceousmaterial. The burned tar gas may travel through the same path as theexhaust gas path 124, but the second heat exchanger may alternativelyinclude a separate burned tar gas path that is substantially similar tothe exhaust gas path 124. This alternative heat source may be used inconjunction with the exhaust gas for pyrolysis, but may alternatively beused independently of the exhaust gas. In particular, in certain usagescenarios, the gaseous fuel output may not be used in an engine, theengine may not be coupled to the downdraft gasifier 100, or the enginemay malfunction. In such usage scenarios, the burned tar gas may be usedas the heat source for pyrolysis, substantially eliminating thedependency on the engine. However, any other suitable heat transfer andtemperature relationship within the second heat exchanger 220 may beused.

The reactor module 130 is preferably where the tar gas is combusted andthe combusted tar gas is reduced with the charcoal. More specifically,the tar gas is put into contact with oxygen at combustion temperaturesto combust, and the combusted tar gas is put into contact with thecharcoal to reduce into carbon monoxide (CO) and hydrogen (H₂), whichcan then be used as gaseous fuel. As described above, the tar gas andcharcoal enters the reactor module 130 from the tar gas and charcoaloutlet 128 of the pyrolysis module 120. The reactor module 130 ispreferably of the Imbert reactor type, but may alternatively be anyother suitable reactor type. The reactor module 130 is preferably placedinside a gas cowling 132 that substantially envelops the reactor module130. The gas cowling 132 is also preferably composed of sheet metal,flange rings, and end plates that maintain the shape and fasten the gascowling to the reactor module 130. The gas cowling 132 preferablyaccommodates to a variety of types of reactors. The gas cowling 132 andthe reactor module 130 preferably cooperate to define an annular spacebetween the reactor module 130 and the gas cowling 132. The gaseous fueloutlet 131 of the reactor module 130 is preferably located at the bottomof the reactor module such that the gaseous fuel exits after thereduction reaction from the bottom of the reactor and is directedupwards and around the reactor module 130 by the gas cowling 132. Theannular space between the reactor module 130 and the gas cowling 132preferably includes a gaseous fuel outlet 134 located substantially nearthe top of the gas cowling that outputs the gaseous fuel to the dryingmodule 130, heat extractor 140, the cyclone module 142, and/or thefourth heat exchanger 240. However, any other arrangement suitablearrangement of the reactor module 130 may be used.

The third heat exchanger 230 is preferably arranged substantially withinthe annual space defined by the reactor module 130 and the gas cowling132. As described above, the gaseous fuel output is directed to flow upand around the reactor module 130 within the annular space substantiallyfrom the bottom of the gas cowling 132 up to the substantially the topof the gas cowling. The third heat exchanger 230 utilizes this flow ofthe gaseous fuel to preheat the air used to combust the tar gas withinthe reactor module 130. As shown in FIG. 3, the first heat exchangerpreferably includes an air inlet 232, an air path 234, and an air outlet236. The air inlet 232 preferably receives air, for example, ambient airor any other suitable air that includes a suitable amount of oxygen. Theair inlet 232 is preferably located substantially near the top of thegas cowling 132. The air path 234 preferably traverses about the reactormodule 130 at least once, for example, the air path 234 is defined bythermally conductive tubing (for example, steel tubing) that is wrappedaround the reactor module 130 at least one revolution directed towardsthe bottom of the gas cowling 132, however, any other suitable materialor method may be used to define the air path 234. By allowing the airpath to revolve around the reactor module 130, the air path 234 islengthened (as compared to an air path that travels substantially in astraight line from the top to the bottom of the gas cowling 132) andtotal heat transfer within the third heat exchanger 230 is substantiallyincreased. The air outlet 236 is preferably coupled to the interior ofthe reactor module 130, as shown in FIG. 3, injecting air and allowingcombustion (and subsequently, reduction) of the tar gas. As describedabove, the gaseous fuel output of the reactor is traveling upwardswithin the same annular space where the air path 234 is contained. Thisallows for the gaseous fuel output to heat the air within the air path234 prior to injection into the reactor module 130. In other words, thethird heat exchanger 230 recaptures the heat energy from gaseous fueloutput of the reactor module 130 and reuses it in the reactor module130, potentially providing a significant increase in energy productionefficiency of the downdraft gasifier 100. As shown in FIG. 3, the airpath 234 wraps around substantially the bottom of the reactor module 130prior to entering the interior of the reactor module 130, allowing theair path 234 to traverse substantially the entire length of the gascowling 132/reactor module 130, further increasing the distance overwhich the gaseous fuel output of the reactor module 130 can transferheat to the air. This arrangement of the flow of air and gaseous fueloutput substantially increases the output temperature of the air throughthe air outlet 236 and substantially decreases the output temperature ofthe gaseous fuel outlet 134 of the gas cowling 132. Additionally, as aresult of the heat transfer, the temperature of the reactor module 130is substantially lower at the top than at the bottom, allowing thepyrolysis module 120 to be inserted into the reactor module 130 withoutsubstantial heat transfer from the reactor module 130 to the pyrolysismodule 120 and facilitating transport of tar gas and charcoal into thereactor module 130.

By locating the gaseous fuel outlet from the reactor module 130substantially at the bottom of the gas cowling 132, the gaseous fueloutlet 134 from the gas cowling substantially at the top of the gascowling 132, the air inlet 232 substantially at the top of the gascowling 132, and routing the air path 234 substantially to the bottom ofthe gas cowling 132, counter current flow is induced between the gaseousfuel output from the reactor module 130 and the air within the air path234. This counter current flow is beneficial for heat transfer.Additionally, as the gaseous fuel output flows across the air path 234,turbulence is introduced into the gaseous fuel output flow, which mayimprove particulate separation from gaseous fuel, cleaning the gaseousfuel. As described above, the gaseous fuel output after reduction may beat a temperature around 600° C. Through the third heat exchanger 230,the gaseous fuel output may be decreased to a temperature in the rangeof 200° C.-300° C. However, the third heat exchanger 230 may decreasethe temperature even more, decreasing the need for the heat extractor140. However, any other suitable heat transfer and temperaturerelationship within the third heat exchanger may be used.

As shown in FIG. 3, the gas cowling 132 may also include a sedimentcollector 136 located below the reactor module 130 that collectsparticulates that are extracted from the gaseous fuel and/or the ashthat results from the charcoal after the combusted tar gas is reducedwith the charcoal. The sediment collector 132 is preferably removable toallow for the sediments to be disposed of after use. However, any othersuitable arrangement of the sediment collector maybe used.

In the preferred embodiments, the downdraft gasifier further includes aheat extractor 140 that further extracts heat from the gaseous fueloutput prior to using the heat to dry the carbonaceous material. Theheat extractor 140 may be a radiator that radiates out heat from thegaseous fuel output to the ambient environment. The heat extractor 140preferably includes a gaseous fuel input 144 that receives gaseous fuelfrom the gaseous fuel outlet 134 of the gas cowling 132 and a gaseousfuel output 146 that is coupled to the gaseous fuel inlet 212 of thefirst heat exchanger 210. As shown in FIG. 3, the heat extractor 140 mayinclude a cyclone module 142 that functions to further extractparticulates from the gaseous fuel output. In the process of routing thegaseous fuel through the cyclone module 142, heat is radiated out intothe ambient environment. The heat extractor 140 and/or the cyclonemodule 142 may also include heat radiating features (for example, heatfins) that facilitate the extraction of heat from the gaseous fueloutput. The heat extractor 140 and/or the cyclone module 142 ispreferably arranged substantially underneath the first heat exchanger210 to utilize the tendency for hot gas to rise to direct the gaseousfuel into the first heat exchanger 210. However, any other suitablearrangement of the heat extractor and/or the cyclone module 142 may beused.

Alternatively, the heat extractor 140 may include a fourth heatexchanger 240 that uses the heat energy from the gaseous fuel to dowork, for example, to heat water. In a first variation, the fourth heatexchanger includes a water inlet 242, a water path 244, and a wateroutlet 246. The water inlet preferably receives water from a watersource. The water path preferably traverses about the heat extractor 140and/or cyclone 142 and the gaseous fuel is used to heat the water. Thetemperature of the gaseous fuel may be high enough to vaporize thewater, allowing steam to exit through the water outlet. The introductionof water in the reduction process may increase the amount of usablegaseous fuel that is produced in the gasifier without increasing theamount of carbonaceous material used. Increasing the amount ofcarbonaceous material increases the amount of air that is used ingaseous fuel production, which may increase the nitrogen content withinthe gaseous fuel and dilute the usable gaseous fuel. Thus, introducingsteam into the reactor may produce higher quality gaseous fuel.Additionally, the introduction of steam into combustion may alsoprovided added benefits of reducing soot reduction and facilitatingcombustion. The water outlet may alternatively be coupled to the airpath 234 of the third heat exchanger 230. In this variation of thefourth heat exchanger 240, heat is recaptured from the gaseous fueloutput of the reactor module 130 and reused in the reactor module 130(through the production of steam and injection of the steam),potentially providing a significant increase in energy productionefficiency of the downdraft gasifier 100. A second variation of thefourth heat exchanger 240 is substantially similar to the firstvariation. In the second variation, the water source for the fourth heatexchanger 240 is the water content that is removed from the carbonaceousmaterial in the dryer module no. As described above, water is collectedin the condensing portion 112 of the dryer module no. In this variation,the condensing portion 112 may include a water outlet that is coupled tothe water inlet of the fourth heat exchanger to be heated and/orinjected into the reactor. In addition to recycling the water contentwithin the system, the water collected in the dryer module was alsoheated by heat from the gaseous fuel output, thus adding another layerof recapturing and reusing thermal energy within the downdraft gasifierDm. However, any other suitable arrangement, heat transfer, material,and temperature relationship for the heat extractor 140 may be used.

In addition to increasing efficiencies through heat and materialrecycling, the downdraft gasifier 100 of the preferred embodiments alsosubstantially isolates major chemical reactions from each other, asdescribed above, which decreases unnecessary thermal load and mayproduce cleaner gaseous fuel. For example, unnecessary water content inthe pyrolysis process and combustion process becomes a thermal load andmay decrease the efficiency of both processes. Similarly, heat fromhigher temperature reactions is substantially isolated from enteringlower temperature reactions, which may improve quality of the gaseousfuel output. Similarly, poorly managing heat within the reactor andallowing heat to escape the reactor (for example, into the pyrolysis ordrying processes) may decrease the efficiency of combustion andreduction. The connections between each of the modules are preferablysubstantially short while maintaining substantial isolation betweenmodules and heat exchangers to decrease heat loss as materials movebetween modules and heat exchangers. Similarly, each of the modules andheat exchangers may include insulation to further prevent undesired heatloss (as well as to protect a user that may come into contact with asurface of the downdraft gasifier 100.

The downdraft gasifier 100 of the preferred embodiments is preferably ofone of the variations as described above, but may alternatively be anyother suitable arrangement of the processes of gasification thatutilizes heat exchange relationships as described above or any othersuitable variation of heat exchange relationships as described above.For example, it is conceivable that the dryer module 110 and thepyrolysis module 120 may be combined into a dryer/pyrolysis module 121,as shown in FIG. 11, that includes a condensing portion above apyrolysis portion. Heat from the gaseous fuel output and the exhaust ofthe engine may be cooperatively used to vaporize water from thecarbonaceous material that is inserted into the dryer/pyrolysis module.The vaporized water then condenses on the condensing portion above thepyrolysis portion and the combined heat energy is used to pyrolyze thedried carbonaceous fluid. However, any other suitable variation may beused.

As described above, the components of the downdraft gasifier 100 of thepreferred embodiments are each substantially interconnected with asubstantial amount of heat and material recycling that addresses many ofthe hurdles of using downdraft gasification to produce cleaner gaseousfuel relative to updraft gasification and provides a viable solution fordowndraft gasification as a renewable and sustainable energy source. Thedowndraft gasifier 100 of the preferred embodiments provides a powerfulnew method and system for thermally integrating waste heats within agasifier and/or engine to drive gasification to produce additionalgaseous fuel. The downdraft gasifier 100 is also made of substantiallysimple components, allowing construction to be relatively simple,inexpensive, and small scale, which may encourage users to build and usethe downdraft gasifier 100 as a personal energy source.

As a person skilled in the art will recognize from the previous detaileddescription and from the figures and claims, modifications and changescan be made to the preferred embodiments of the invention withoutdeparting from the scope of this invention defined in the followingclaims.

I claim:
 1. A downdraft gasifier system for producing a gaseous fuelfrom a carbonaceous material, the downdraft gasifier system comprising:a dryer module; a pyrolysis module; a reactor module defining acombustion zone and a reduction zone, the reactor module comprising anair path fluidly connecting an oxygen source to the combustion zone of areactor module interior, and a gaseous fuel outlet fluidly connected tothe reduction zone; an engine comprising an engine inlet and an exhaustoutlet; and a heat exchanger system comprising: a first heat exchangerthermally coupled to and fluidly separated from the dryer module, thefirst heat exchanger fluidly coupled between the gaseous fuel outlet andthe engine inlet; a second heat exchanger thermally coupled to andfluidly isolated from the pyrolysis module, fluidly coupled to theengine exhaust; and a third heat exchanger thermally coupled to andfluidly separated from the air path, the third heat exchanger fluidlycoupled between the gaseous fuel outlet and the first heat exchanger. 2.The downdraft gasifier of claim 1, further comprising a heat extractorthat further extracts heat from the gaseous fuel from the reactor moduleprior to the first heat exchanger.
 3. The downdraft gasifier of claim 2,wherein the heat extractor includes a cyclone module that cooperateswith the dryer module, pyrolysis module, and the reactor module tofurther extract particulates and heat from the gaseous fuel from thereactor module, wherein the cyclone includes a gaseous fuel inlet thatreceives gaseous fuel from the reactor module, a gaseous fuel pathwithin the cyclone module that extracts heat and particulates from thegaseous fuel, and a gaseous fuel outlet that delivers gas to the firstheat exchanger.
 4. The downdraft gasifier of claim 2, wherein the heatextractor further includes a fourth heat exchanger that exchanges heatwith the gaseous fuel to extract heat from the gaseous fuel.
 5. Thedowndraft gasifier of claim 4, wherein the fourth heat exchanger heatswater with the gaseous fuel to extract heat from the gaseous fuel. 6.The downdraft gasifier of claim 5, wherein the carbonaceous material isdried by extracting water content in the carbonaceous material, andwherein the fourth heat exchanger heats the water extracted from thecarbonaceous material.
 7. The downdraft gasifier of claim 5, wherein thefourth heat exchanger includes a water inlet that receives water, awater path substantially isolated from the gaseous fuel, and a wateroutlet.
 8. The downdraft gasifier of claim 7, wherein fourth heatexchanger substantially vaporizes the water with the heat from thegaseous fuel and wherein the water outlet outputs water vapor into thereactor module.
 9. The downdraft gasifier of claim 7, wherein thegaseous fuel path traverses about the cyclone module at least once. 10.The downdraft gasifier of claim 9, wherein the gaseous fuel pathrevolves about the cyclone module at least once.
 11. The downdraftgasifier of claim 1, wherein the dryer module substantially isolatesdrying from pyrolyzing, and wherein the pyrolysis module substantiallyisolates pyrolyzing from combusting and reducting.
 12. The downdraftgasifier of claim 11, wherein the dryer module includes a drying portionand a condensing portion arranged substantially above the dryingportion, wherein the dryer module vaporizes the water content in thecarbonaceous material in the drying portion and condenses the risingwater vapor in the condensing portion away from the carbonaceousmaterial, thereby drying the carbonaceous material and substantiallyisolating drying from pyrolyzing.
 13. The downdraft gasifier of claim11, wherein the pyrolysis module is arranged above the reactor andincludes a tar gas and charcoal outlet that is coupled to the reactor,and wherein the reactor receives the tar and charcoal from the tar gasand charcoal outlet of the pyrolysis module.
 14. The downdraft gasifierof claim 13, wherein the tar gas and charcoal outlet includes a motorthat drives the tar gas and charcoal outlet into the reactor.
 15. Amethod for managing heat within a downdraft gasifier for producing agaseous fuel from a carbonaceous material to be used in an engine,comprising the steps of: drying the carbonaceous material with the heatfrom the gaseous fuel output in a dryer module to produce driedcarbonaceous material; pyrolyzing the dried carbonaceous material withthe heat from the exhaust of the engine in a pyrolysis module to producetar gas and charcoal; combusting the tar gas with air and reducing thecombusted tar gas with the charcoal in a reactor module to producegaseous fuel; preheating the air used to combust the tar gas with thegaseous fuel post reduction; and extracting heat and particulates fromthe gaseous fuel post reduction prior to using the heat from the gaseousfuel to dry the carbonaceous material.
 16. The method of claim 15,wherein the step of extracting heat and particulates from the gaseousfuel post reduction includes the step of extracting heat andparticulates from the gaseous fuel in a cyclone module.
 17. The methodof claim 15, wherein the step of extracting heat from the gaseous fuelpost reduction includes vaporizing water with the heat from the gaseousfuel post reduction and injecting the vaporized water into the reactormodule.
 18. The method of claim 17, wherein the step of drying thecarbonaceous material includes extracting water from the carbonaceousmaterial, and wherein the step of vaporizing water includes vaporizingthe water extracted from the carbonaceous material.
 19. The method ofclaim 15, further comprising the steps of substantially isolating thedrying carbonaceous material from the pyrolyzing carbonaceous materialand substantially isolating the pyrolyzing carbonaceous material fromthe combusting tar gas and the reducing charcoal.
 20. The method ofclaim 15, further comprising the step of substantially isolating gaseousfuel output from the carbonaceous material in the dryer module whileallowing heat exchange between the gaseous fuel output and thecarbonaceous material and substantially isolating exhaust gas from thedried carbonaceous material in the pyrolysis module while allowing heatexchange between the exhaust gas and the dried carbonaceous material.